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Before humans settled on the Indian Ocean islands, two distinct groups of giant tortoises could be found there: the Seychelles islands tortoises and the Mascarene islands tortoises, with several different species among the islands. Mauritius and Rodrigues each had two species, while Reunion had a single species. These animals were of two types: the saddleback tortoise, with a long neck for browsing and the some-shaped tortoise which had a shorter neck and was a grazer. It is believed that Mauritius and Rodrigues each had one species of each type: Cylindrapsis inepta and C. triserrata;C. peltastes and C. vosmaeri, respectively), whilst Reunion had a dome-shaped species only (C. indica). The density of tortoises was reported to be the highest in the world, and these animals played a key role in the ecosystem as grazers, browsers and seed dispersers. However, with man’s arrival on the Mascarene Islands, the tortoises were harvested as a food source and their young were killed by introduced animals such as pigs, cats, dogs and rats. It is likely that the last Mascarene tortoise was collected from Round Island in 1844. The sole surviving species of giant tortoise in the Indian Ocean is the Aldabra Giant Tortoise from the Seychelles.

In the process of habitat restoration it is critical that missing ecological interactions are restored as fully as possible. Where the missing interaction is related to a species that has become extinct, analogue species can be used instead – these are closely related species that can fulfill the same environmental role. At MWF we have pioneered the process of replacing an extinct species with an introduced one (re-wilding), using the Aldabra Giant Tortoise Dipsochelys (Aldabrachelys) gigantea to fill the missing browsing, grazing and seed dispersal roles.

In 2000, as part of ongoing restoration work on Ile aux Aigrettes, MWF released 20 Aldabran tortoises on the island and by 2004 they were allowed to roam completely free. The aim was that the tortoises would eat the ebony fruit and then disperse the seeds around the island in their droppings, encouraging the spread of these rare trees naturally. This strategy has been successful, not just because ebony trees are being spread across the island, but also the seeds that they spread have been found to germinate more successfully because they had passed through the tortoise’s gut before being expelled. The tortoises are also breeding on the island and the baby tortoises are regularly taken from Ile aux Aigrettes to the Gerald Durrell Endemic Wildlife Sanctuary (GDEWS) where they are reared in safety until their release back into the wild.

In 2007, as part of a PhD study, 12 sub-adult Aldabran Giant Tortoises and 12 Madagascan Radiated Tortoises, a species also suitable to act as an analogue, were translocated to Round Island. After encouraging results, more were released in 2010/11, reaching a total of 125 released animals. Additional releases are planned in the future. Monitoring is ongoing, regarding both the health and growth of the animals, as well as vegetation surveys, to ensure the continuing success of the programme.

The project is supported in kind by the National Parks and Conservation Service by the provision of the captive breeding centre facility at Black River for rearing the tortoises and for transport and field station facilities on Round Island.